题目来源
https://leetcode.com/problems/first-missing-positive/
Given an unsorted integer array, find the first missing positive integer.
For example,
Given [1,2,0] return 3,
and [3,4,-1,1] return 2.
Your algorithm should run in O(n) time and uses constant space.
题意分析
Input:a list with many numbers
Output:the first missing positive number
Conditions:最小的missing 正整数，注意要0（n）级别的算法
题目思路
利用字典去做，因为字典查询是0（n）的，不过会使用0（n）的空间，AC了，但是网上说要用triky，可能是leecode评测放宽了……以后再回来看看
AC代码（Python）
_author_ = "YE"
# -*- coding:utf-8 -*- class Solution(object):
def firstMissingPositive(self, nums):
"""
:type nums: List[int]
:rtype: int
"""
len1 = len(nums)
if len1 == 0:
return 1
dic = {}
for num in nums:
if num > 0:
dic[num] = num
for i in range(1, len1 + 1):
if dic.get(i, -1) == -1:
return i
return len1 + 1